In my experience, your results are a function of the scanning software
that comes with your HP scanner.
I once had a HP Scanjet 4c that could optionally prescan a page and let
me select the area that I actually wanted to scan into Word. Took a bit
longer because each page got scanned twice (scanner does a preview scan,
I select an area, scanner scans to Word). The Scanjet 4c could also
scan a preset letter- or A4-size area.
A coworker had a different HP scanner (an all-in-one
printer/scanner/fax/copier thing) that would only scan a preset letter-
or A4-size area (even if the page wasn't that big) and insert that into
Word. If yours functions in this way, then in Word you can manually
crop the unwanted white space around the image on each page, and resize
the remainder to fill the page. In Word 2003 or earlier, you'll find a
Crop tool on the Drawing toolbar (View | Toolbars | Drawing). In Word
2007, click on a scanned image, and click on Picture Tools: Format |
Crop.